Ultrasound assisted crystallisation of synthetic gypsum

Ultrasound assisted crystallisation of synthetic gypsum
from used battery acid
Heven Abdul-Jabbar, Hafid Al-Daffaee, Peter Claise & Phill Lorimer
Coventry University, School of science and the environment, Priory street, Coventry,
ABSTRACT: The production and recycling of lead acid batteries, has a very
important role in the lead industry. The entire lead consumption from battery
production is about 60-70 % depending on a country, although recently the
profitability is reducing due to environmental costs mostly in relation to waste
generation and energy consumption. Very large amounts of toxic leachable soda slugs
are produced for landfill from recycling spent batteries. Therefore developing a zero
waste generating process to produce a new concept in the battery reprocessing
industry is vital and which is the aim of this project.
In this project a scientific and rational model for the production of gypsum that was
validated on a pilot plant scale. Therefore it was necessary to investigate how the
variation in chemical composition will affect the synthetically produced gypsum
quality, i.e. analyzing the gypsum produced for some trace metals, such as Pb, Fe, Cu,
As, Sb, Zn, Ni, Cd and Na. Most of these metals can cause a serious hazard to humans
through inhalation, skin contact, eye contact or ingestion [Rai and Amit ,Jan 2002].
Na is not toxic however it can cause efflorescence and Fe causes discolouration of the
plasterboard. Synthetic gypsum can be produced by a simple chemical reaction
between sulphuric acid (H2SO4) and lime (Ca(OH)2) or limestone (CaCO3). The nonferrous metallurgical industry produces large volumes of acidic effluents, or
wastewaters, which are treated using lime neutralization in order to remove the acidity
and heavy metals. The success of this research lead to investigating the possibility of
making synthetic gypsum during the neutralization of acidic waste waters with lime or
limestone. Gypsum samples were produced at different operational conditions (pH,
temperature, mixer speed, residence time, etc.). The samples were analysed for trace
metal content using flame atomic absorption spectroscopy and inductively coupled
plasma spectrometry.
Ultrasound assisted crystallisation during the synthesis of gypsum was performed to
observe the possibility of obtaining a cleaner gypsum product. A 40 kHz ultrasonic
bath and a 20 kHz ultrasonic probe were used in this investigation. All the
experiments performed in this investigation were lasted for 4 hours and were carried
out at room temperature. Different ultrasonic powers and different methods of
sonication methods were carried out at pH 2 and pH 4 in order to obtain the cleanest
gypsum product. Various sonication methods were also carried out using the 20 kHz
ultrasonic probe at 25%, 50% and 75% sonication powers.